In the operation of a rotary offset printing press, freshly printed substrates, such as sheets or web material, are guided by transfer cylinders or the like from one printing unit to another, and then they are delivered to a sheet stacker or to a sheet folder/cutter unit, respectively. As used herein, the term “transfer cylinder” includes delivery cylinders, transfer rollers, support rollers, support cylinders, delivery wheels, skeleton wheels, segmented wheels, transfer drums, support drums, spider wheels, support wheels, guide wheels, guide rollers, and the like.
The ink marking problems inherent in transferring freshly printed substrates have been longstanding. In order to minimize the contact area between the transfer means and the freshly printed substrate, conventional support wheels have been modified in the form of relatively thin disks having a toothed or serrated circumference, referred to as skeleton wheels. However, those thin disc transfer means have not overcome the problems of smearing and marking the freshly printed substrate due to moving contact between the freshly printed substrate and the projections or serrations. Moreover, the attempts to cover the transfer cylinder with a cover material and/or minimize the surface support area in contact with the freshly printed substrate material often resulted in further problems.
Various efforts have been made to overcome the limitations of thin disk skeleton wheels. One of the most important improvements has been completely contrary to the concept of minimizing the surface area of contact. That improvement is disclosed and claimed in U.S. Pat. No. 3,791,644 to Howard W. DeMoore, incorporated by reference herein in its entirety, wherein the support surface of a transfer cylinder in the form of a wide wheel or cylinder is coated with an improved ink repellent surface formed by a layer of polytetrafluoroethylene (PTFE).
During the use of the PTFE coated transfer cylinders in high-speed commercial printing presses, the surface of the coated cylinders must be washed frequently with a solvent to remove any ink accumulation. Moreover, it has also been determined that the PTFE coated cylinders do not provide a cushioning effect and relative movement, which are beneficial.
The limitations on the use of the PTFE coated transfer cylinders have been overcome with an improved transfer cylinder having an ink repellent, cushioning, and supportive fabric covering or the like for transferring the freshly printed sheet. It is now well recognized and accepted in the printing industry world-wide that marking and smearing of freshly printed sheets caused by engagement of the wet printed surface with the supporting surface of a conventional press transfer cylinder is substantially reduced by using the anti-marking fabric covering system as disclosed and claimed in U.S. Pat. No. 4,402,267 entitled “Method and Apparatus for Handling Printed Sheet Material,” the disclosure of which is incorporated herein by reference.
That system, which is marketed under license by Printing Research, Inc. of Dallas, Tex., U.S.A. under the registered trademark SUPER BLUE® includes the use of a low friction coating or coated material on the supporting surface of the transfer cylinder, and over which is loosely attached a movable fabric covering. The fabric covering provided a yieldable, cushioning support for the freshly printed side of the substrate such that relative movement between the freshly printed substrate and the transfer cylinder surface would take place between the fabric covering and the support surface of the transfer cylinder so that marking and smearing of the freshly printed surface was substantially reduced. Various improvements have been made to the SUPER BLUE® system, which are described in more detail in U.S. Pat. Nos. 5,907,998 and 6,244,178 each entitled “Anti-Static, Anti-Smearing Pre-Stretched and Pressed Flat, Precision-Cut Striped Flexible Coverings for Transfer Cylinders”; U.S. Pat. Nos. 5,511,480, 5,603,264, 6,073,556, 6,119,597, and 6,192,800 each entitled “Method and Apparatus for Handling Printed Sheet Material”; U.S. Pat. No. 5,979,322 entitled “Environmentally Safe, Ink Repellent, Anti-Marking Flexible Jacket Covering Having Alignment Stripes, Centering Marks and Pre-Fabricated Reinforcement Strips for Attachment onto Transfer Cylinders in a Printing Press”; and U.S. Pat. No. RE39,305 entitled “Anti-static, Anti-smearing Pre-stretched and Pressed Flat, Precision-cut Striped Flexible Coverings for Transfer Cylinders,” each of which is hereby incorporated by reference herein in its entirety. The above cited patents were assigned by Howard W. DeMoore to Printing Research, Inc. of Dallas, Tex., USA and are all owned by Printing Research, Inc.